The concept of pressure relief valves is known in the art. Generally, pressure relief valves have a pressure responsive mechanism that senses when the fluid pressure in a system has exceeded a predetermined pressure. When the predetermined pressure is exceeded, the relief valve opens to allow fluid to escape and consequently allow the internal system pressure to decrease to a safe condition. One of the difficulties with pressure relief valves is that even though the valve may function property to allow high pressure fluid to escape from the system it is difficulty to seal the valve or maintain the valve in a sealed condition if the normal operating pressure difference between the external system pressure and the internal system pressure is low, for example a pressure differential on the order of a few inches of water. When the internal system pressure decreases to a condition where the internal system pressure is only slightly greater than the external system pressure there is a tendency for the pressure relief valve seals to leak thus allowing fluid to slowly escape from the system. Generally, a one time discharge of fluid when the system is over pressurized condition can create a nuisance but can be dealt with. On the other hand, if the pressure relief valve cannot seal properly at low pressure differentials one may have a continuous release of fluidized materials from the system. If the system contain harmful or toxic materials a continuous release creates a hazardous condition. The present invention provides a pressure relief valve with a first sealing member in a cantilevered sealing arrangement that allows the pressure relief valve to seat and remain seated at extremely low differential pressures, yet allows the pressure relief valve to open to discharge fluid if the differential pressure exceeds a predetermined differential pressure.
In addition, in a further embodiment of the invention the pressure relief valve includes a second sealing member in a second cantilevered scaling arrangement with the second sealing member maintained in a sealing condition when the internal system pressure exceeds the external system pressure but if the external system pressure exceeds the internal system pressure by a second predetermined pressure the second sealing arrangement allows the second sealing member to open to allow fluid to enter the system thereby equalizing the fluid pressure differential forces in the system.